diff --git a/include/private/ui/LayerState.h b/include/private/ui/LayerState.h
index b6fcd80..f1a2618 100644
--- a/include/private/ui/LayerState.h
+++ b/include/private/ui/LayerState.h
@@ -25,8 +25,6 @@
 #include <ui/ISurfaceFlingerClient.h>
 #include <ui/Region.h>
 
-#include <private/ui/SharedState.h>
-
 namespace android {
 
 class Parcel;
diff --git a/include/private/ui/SharedBufferStack.h b/include/private/ui/SharedBufferStack.h
new file mode 100644
index 0000000..2bd5344
--- /dev/null
+++ b/include/private/ui/SharedBufferStack.h
@@ -0,0 +1,327 @@
+/*
+ * Copyright (C) 2007 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_UI_SHARED_BUFFER_STACK_H
+#define ANDROID_UI_SHARED_BUFFER_STACK_H
+
+#include <stdint.h>
+#include <sys/types.h>
+
+#include <cutils/compiler.h>
+
+#include <utils/Debug.h>
+#include <utils/threads.h>
+#include <utils/String8.h>
+
+#include <ui/Rect.h>
+
+namespace android {
+// ---------------------------------------------------------------------------
+
+/*
+ * These classes manage a stack of buffers in shared memory.
+ * 
+ * SharedClient: represents a client with several stacks
+ * SharedBufferStack: represents a stack of buffers
+ * SharedBufferClient: manipulates the SharedBufferStack from the client side 
+ * SharedBufferServer: manipulates the SharedBufferStack from the server side 
+ *
+ * Buffers can be dequeued until there are none available, they can be locked
+ * unless they are in use by the server, which is only the case for the last 
+ * dequeue-able buffer. When these various conditions are not met, the caller
+ * waits until the condition is met.
+ *
+ * 
+ * CAVEATS:
+ * 
+ * In the current implementation there are several limitations:
+ * - buffers must be locked in the same order they've been dequeued
+ * - buffers must be enqueued in the same order they've been locked
+ * - dequeue() is not reentrant
+ * - no error checks are done on the condition above
+ * 
+ */
+
+// When changing these values, the COMPILE_TIME_ASSERT at the end of this
+// file need to be updated.
+const unsigned int NUM_LAYERS_MAX  = 31;
+const unsigned int NUM_BUFFER_MAX  = 4;
+const unsigned int NUM_DISPLAY_MAX = 4;
+
+// ----------------------------------------------------------------------------
+
+class Region;
+class SharedBufferStack;
+class SharedClient;
+
+// ----------------------------------------------------------------------------
+
+struct FlatRegion { // 12 bytes
+    static const unsigned int NUM_RECT_MAX = 1;
+    uint32_t    count;
+    uint16_t    rects[4*NUM_RECT_MAX];
+};
+
+// should be 128 bytes (32 longs)
+class SharedBufferStack
+{
+    friend class SharedClient;
+    friend class SharedBufferBase;
+    friend class SharedBufferClient;
+    friend class SharedBufferServer;
+
+public:
+    SharedBufferStack();
+    status_t setDirtyRegion(int buffer, const Region& reg);
+    Region getDirtyRegion(int buffer) const;
+
+    // these attributes are part of the conditions/updates
+    volatile int32_t head;      // server's current front buffer
+    volatile int32_t available; // number of dequeue-able buffers
+    volatile int32_t queued;    // number of buffers waiting for post
+    volatile int32_t inUse;     // buffer currently in use by SF
+
+    // not part of the conditions
+    volatile int32_t reallocMask;
+
+    int32_t     identity;       // surface's identity (const)
+    status_t    status;         // surface's status code
+    int32_t     reserved32[13];
+    FlatRegion  dirtyRegion[NUM_BUFFER_MAX];    // 12*4=48 bytes
+};
+
+// ----------------------------------------------------------------------------
+
+// 4 KB max
+class SharedClient
+{
+public:
+    SharedClient();
+    ~SharedClient();
+
+    status_t validate(size_t token) const;
+    uint32_t getIdentity(size_t token) const;
+    status_t setIdentity(size_t token, uint32_t identity);
+
+private:
+    friend class SharedBufferBase;
+    friend class SharedBufferClient;
+    friend class SharedBufferServer;
+
+    // FIXME: this should be replaced by a lock-less primitive
+    Mutex lock;
+    Condition cv;
+    SharedBufferStack surfaces[ NUM_LAYERS_MAX ];
+};
+
+// ============================================================================
+
+class SharedBufferBase
+{
+public:
+    SharedBufferBase(SharedClient* sharedClient, int surface, int num);
+    ~SharedBufferBase();
+    uint32_t getIdentity();
+    size_t getFrontBuffer() const;
+    String8 dump(char const* prefix) const;
+
+protected:
+    SharedClient* const mSharedClient;
+    SharedBufferStack* const mSharedStack;
+    const int mNumBuffers;
+
+    friend struct Update;
+    friend struct QueueUpdate;
+
+    struct ConditionBase {
+        SharedBufferStack& stack;
+        inline ConditionBase(SharedBufferBase* sbc) 
+            : stack(*sbc->mSharedStack) { }
+    };
+
+    struct UpdateBase {
+        SharedBufferStack& stack;
+        inline UpdateBase(SharedBufferBase* sbb) 
+            : stack(*sbb->mSharedStack) { }
+    };
+
+    template <typename T>
+    status_t waitForCondition(T condition);
+
+    template <typename T>
+    status_t updateCondition(T update);
+};
+
+template <typename T>
+status_t SharedBufferBase::waitForCondition(T condition) 
+{
+    SharedClient& client( *mSharedClient );
+    const nsecs_t TIMEOUT = s2ns(1); 
+    Mutex::Autolock _l(client.lock);
+    while (!condition()) {
+        status_t err = client.cv.waitRelative(client.lock, TIMEOUT);
+        
+        // handle errors and timeouts
+        if (CC_UNLIKELY(err != NO_ERROR)) {
+            if (err == TIMED_OUT) {
+                if (condition()) {
+                    LOGE("waitForCondition(%s) timed out (identity=%d), "
+                            "but condition is true! We recovered but it "
+                            "shouldn't happen." , 
+                            T::name(), mSharedStack->identity);
+                    break;
+                } else {
+                    LOGW("waitForCondition(%s) timed out (identity=%d). "
+                            "CPU may be pegged. trying again.",
+                            T::name(), mSharedStack->identity);
+                }
+            } else {
+                LOGE("waitForCondition(%s) error (%s) ",
+                        T::name(), strerror(-err));
+                return err;
+            }
+        }
+    }
+    return NO_ERROR;
+}
+
+
+template <typename T>
+status_t SharedBufferBase::updateCondition(T update) {
+    SharedClient& client( *mSharedClient );
+    Mutex::Autolock _l(client.lock);
+    ssize_t result = update();
+    client.cv.broadcast();    
+    return result;
+}
+
+// ----------------------------------------------------------------------------
+
+class SharedBufferClient : public SharedBufferBase
+{
+public:
+    SharedBufferClient(SharedClient* sharedClient, int surface, int num);
+    
+    ssize_t dequeue();
+    status_t undoDequeue(int buf);
+    
+    status_t lock(int buf);
+    status_t queue(int buf);
+    bool needNewBuffer(int buffer) const;
+    status_t setDirtyRegion(int buffer, const Region& reg);
+
+private:
+    friend struct Condition;
+    friend struct DequeueCondition;
+    friend struct LockCondition;
+
+    struct QueueUpdate : public UpdateBase {
+        inline QueueUpdate(SharedBufferBase* sbb);
+        inline ssize_t operator()();
+    };
+
+    struct UndoDequeueUpdate : public UpdateBase {
+        inline UndoDequeueUpdate(SharedBufferBase* sbb);
+        inline ssize_t operator()();
+    };
+
+    // --
+
+    struct DequeueCondition : public ConditionBase {
+        inline DequeueCondition(SharedBufferClient* sbc);
+        inline bool operator()();
+        static inline const char* name() { return "DequeueCondition"; }
+    };
+
+    struct LockCondition : public ConditionBase {
+        int buf;
+        inline LockCondition(SharedBufferClient* sbc, int buf);
+        inline bool operator()();
+        static inline const char* name() { return "LockCondition"; }
+    };
+
+    int32_t tail;
+};
+
+// ----------------------------------------------------------------------------
+
+class SharedBufferServer : public SharedBufferBase
+{
+public:
+    SharedBufferServer(SharedClient* sharedClient, int surface, int num);
+
+    ssize_t retireAndLock();
+    status_t unlock(int buffer);
+    status_t reallocate();
+    status_t assertReallocate(int buffer);
+
+    Region getDirtyRegion(int buffer) const;
+
+private:
+    struct UnlockUpdate : public UpdateBase {
+        const int lockedBuffer;
+        inline UnlockUpdate(SharedBufferBase* sbb, int lockedBuffer);
+        inline ssize_t operator()();
+    };
+
+    struct RetireUpdate : public UpdateBase {
+        const int numBuffers;
+        inline RetireUpdate(SharedBufferBase* sbb, int numBuffers);
+        inline ssize_t operator()();
+    };
+
+    struct ReallocateCondition : public ConditionBase {
+        int buf;
+        inline ReallocateCondition(SharedBufferBase* sbb, int buf);
+        inline bool operator()();
+        static inline const char* name() { return "ReallocateCondition"; }
+    };
+};
+
+// ===========================================================================
+
+struct display_cblk_t
+{
+    uint16_t    w;
+    uint16_t    h;
+    uint8_t     format;
+    uint8_t     orientation;
+    uint8_t     reserved[2];
+    float       fps;
+    float       density;
+    float       xdpi;
+    float       ydpi;
+    uint32_t    pad[2];
+};
+
+struct surface_flinger_cblk_t   // 4KB max
+{
+    uint8_t         connected;
+    uint8_t         reserved[3];
+    uint32_t        pad[7];
+    display_cblk_t  displays[NUM_DISPLAY_MAX];
+};
+
+// ---------------------------------------------------------------------------
+
+COMPILE_TIME_ASSERT(sizeof(SharedClient) <= 4096)
+COMPILE_TIME_ASSERT(sizeof(SharedBufferStack) == 128)
+COMPILE_TIME_ASSERT(sizeof(surface_flinger_cblk_t) <= 4096)
+
+// ---------------------------------------------------------------------------
+}; // namespace android
+
+#endif /* ANDROID_UI_SHARED_BUFFER_STACK_H */
diff --git a/include/private/ui/SharedState.h b/include/private/ui/SharedState.h
deleted file mode 100644
index c9f6b5e..0000000
--- a/include/private/ui/SharedState.h
+++ /dev/null
@@ -1,154 +0,0 @@
-/*
- * Copyright (C) 2007 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#ifndef ANDROID_UI_SHARED_STATE_H
-#define ANDROID_UI_SHARED_STATE_H
-
-#include <stdint.h>
-#include <sys/types.h>
-
-#include <utils/Debug.h>
-#include <utils/threads.h>
-
-namespace android {
-
-/*
- * These structures are shared between the composer process and its clients
- */
-
-// ---------------------------------------------------------------------------
-
-struct surface_info_t { // 4 longs, 16 bytes
-    enum {
-        eBufferDirty    = 0x01,
-        eNeedNewBuffer  = 0x02
-    };
-    uint8_t     reserved[11];
-    uint8_t     flags;
-    status_t    status;
-};
-
-// ---------------------------------------------------------------------------
-
-const uint32_t NUM_LAYERS_MAX = 31;
-
-enum { // layer_cblk_t swapState
-    eIndex              = 0x00000001,
-    eFlipRequested      = 0x00000002,
-    
-    eResizeBuffer0      = 0x00000004,
-    eResizeBuffer1      = 0x00000008,    
-    eResizeRequested    = eResizeBuffer0 | eResizeBuffer1,
-    
-    eBusy               = 0x00000010,
-    eLocked             = 0x00000020,
-    eNextFlipPending    = 0x00000040,    
-    eInvalidSurface     = 0x00000080
-};
-
-enum { // layer_cblk_t flags
-    eLayerNotPosted     = 0x00000001,
-    eNoCopyBack         = 0x00000002,
-    eReserved           = 0x0000007C,
-    eBufferIndexShift   = 7,
-    eBufferIndex        = 1<<eBufferIndexShift,
-};
-
-struct flat_region_t    // 40 bytes
-{
-    int32_t     count;
-    int16_t     l;
-    int16_t     t;
-    int16_t     r;
-    int16_t     b;
-    uint16_t    runs[14];
-};
-
-struct layer_cblk_t     // (128 bytes)
-{
-    volatile    int32_t             swapState;      //  4
-    volatile    int32_t             flags;          //  4
-    volatile    int32_t             identity;       //  4
-                int32_t             reserved;       //  4
-                surface_info_t      surface[2];     // 32
-                flat_region_t       region[2];      // 80
-
-    static inline int backBuffer(uint32_t state) {
-        return ((state & eIndex) ^ ((state & eFlipRequested)>>1));
-    }
-    static inline int frontBuffer(uint32_t state) {
-        return 1 - backBuffer(state);
-    }
-};
-
-// ---------------------------------------------------------------------------
-
-struct per_client_cblk_t   // 4KB max
-{
-    per_client_cblk_t() : lock(Mutex::SHARED) { }
-
-                Mutex           lock;
-                Condition       cv;
-                layer_cblk_t    layers[NUM_LAYERS_MAX] __attribute__((aligned(32)));
-
-    enum {
-        BLOCKING = 0x00000001,
-        INSPECT  = 0x00000002
-    };
-
-    // these functions are used by the clients
-    status_t validate(size_t i) const;
-    int32_t lock_layer(size_t i, uint32_t flags);
-    uint32_t unlock_layer_and_post(size_t i);
-    void unlock_layer(size_t i);
-};
-// ---------------------------------------------------------------------------
-
-const uint32_t NUM_DISPLAY_MAX = 4;
-
-struct display_cblk_t
-{
-    uint16_t    w;
-    uint16_t    h;
-    uint8_t     format;
-    uint8_t     orientation;
-    uint8_t     reserved[2];
-    float       fps;
-    float       density;
-    float       xdpi;
-    float       ydpi;
-    uint32_t    pad[2];
-};
-
-struct surface_flinger_cblk_t   // 4KB max
-{
-    uint8_t         connected;
-    uint8_t         reserved[3];
-    uint32_t        pad[7];
-    display_cblk_t  displays[NUM_DISPLAY_MAX];
-};
-
-// ---------------------------------------------------------------------------
-
-COMPILE_TIME_ASSERT(sizeof(layer_cblk_t) == 128)
-COMPILE_TIME_ASSERT(sizeof(per_client_cblk_t) <= 4096)
-COMPILE_TIME_ASSERT(sizeof(surface_flinger_cblk_t) <= 4096)
-
-// ---------------------------------------------------------------------------
-}; // namespace android
-
-#endif // ANDROID_UI_SHARED_STATE_H
-
diff --git a/include/private/ui/SurfaceBuffer.h b/include/private/ui/SurfaceBuffer.h
index bf68406..73e517b 100644
--- a/include/private/ui/SurfaceBuffer.h
+++ b/include/private/ui/SurfaceBuffer.h
@@ -47,6 +47,9 @@
     status_t lock(uint32_t usage, const Rect& rect, void** vaddr);
     status_t unlock();
 
+    void setIndex(int index);
+    int getIndex() const;
+    
 protected:
             SurfaceBuffer();
             SurfaceBuffer(const Parcel& reply);
@@ -69,6 +72,7 @@
             android_native_buffer_t const* buffer);
     
     BufferMapper& mBufferMapper;
+    int mIndex;
 };
 
 }; // namespace android